|
Current generation radars employ a first order approximation to compensate the frequency shift due to target's velocity.
This approach is inadequate when high velocity targets are considered; however, real targets do not possess such high
velocities. For that reason, this research analyzes how the increment of the Time-Bandwidth (TBW) product and the
target velocity would impact the analysis of radar signals when a first order approximation is implemented to
compensate the Doppler shift. The common approach to improved resolution and performance of radar system is to
increase the time-bandwidth product of the transmitted signal. The problem of using the first order approximation to
compensate the Doppler is that it is limited only to the first two terms of a power series expansion of a full Doppler
compensation. As a consequence, an increment on the target's velocity or the time-bandwidth product of the transmitted
signal will result in a significant error at the output of the matched filter.
On this research a Linear FM (chirp) signal with a large TBW is considered as the transmitted signal. First, to observe
the effects of increasing the time-bandwidth product and target velocity the received signal is modeled using a full
Doppler compensation and a first order approximation. Second, each signal is applied to the input of one matched filter
in which the transmitted signal is used as a reference. Finally, the outputs from both matched filters are analyzed in order
to observe the effects of using the first order approximation to model the Doppler induced on the reflected signal. This
analysis was performed assuming that the target was moving at a constant velocity. By increasing the time-bandwidth
product of the transmitted signal the output of both matched filters are compared and analyzed to observe the differences
between modeling the reflected signal using the first order compensation and the full Doppler compensation. The
simulation results showed that, by increasing the time-bandwidth product of the transmitted signal the output of the
matched filter using the first order approximation deviates significantly with respect to the matched filter that contains
the signal modeled using the full Doppler compensation. From these results it is concluded that a dramatic increase in
time-bandwidth product of the received signal, results in a significant error at the output of the matched filter if the first
order approximation is used to model the reflected signal instead of the Full Doppler compensation.
|
